Lecanora cinereofusca has a
thallus (the main body of the lichen) that is continuous or irregularly cracked (), varying from pale to medium grey in colour with a smooth to warted surface. The (the initial fungal growth area) is either absent or appears black. The reproductive structures (
apothecia) measure 0.7–1.5 mm in diameter and are initially immersed in the thallus, sometimes becoming (attached directly to the surface) as they mature. The (the rim around the apothecium derived from the thallus) is well-developed and persistent, with a coarsely scalloped to almost toothed edge that becomes wavy with age. This margin is white or a paler grey than the surrounding thallus and contains very large crystals that do not dissolve in
potassium hydroxide solution (
K). The of the apothecium is flat to slightly convex and orange-brown or red-brown in colour. The (the uppermost layer of the apothecium) is red-brown, containing coarse that are also present on the surface. These granules do not dissolve in K but turn orange when treated with
para-phenylenediamine (Pd+), forming crystals in the process. The
hymenium (the spore-producing layer) is 60–85 μm tall. The
paraphyses (sterile filaments among the reproductive cells) are 2–3 μm in diameter, sparsely branched and interconnected, with tips that are not or only slightly swollen. (sexual spores produced in asci) made by
L. cinereofusca are broadly
ellipsoidal, typically measuring 10–14.5 by 7–8.5 μm. The
conidia (asexual spores) are cylindrical and 10–14 μm long. When subjected to chemical
spot tests, the thallus is C−, K+ (yellow), Pd−, and fluoresces mauve-purple under
ultraviolet light (UV+). Both the thalline margin and epithecium turn yellow-orange when treated with Pd. The lichen contains several
secondary metabolites including
atranorin,
pannarin, and sometimes
placodialic acid and
roccellic acid. ==Habitat and distribution==